The present invention relates to a braking torque regulator for a vehicle having a braking energy recovery arrangement that is able to generate a first braking torque that may not exceed a maximum first braking torque, and a mechanical brake system that is able to generate a second braking torque. The present invention also relates to a method for regulating a braking torque in a vehicle of this type. The present invention further relates to circuitry for a braking force regulator in a vehicle that has a braking energy recovery arrangement.
In vehicles with a braking energy recovery arrangement, a first braking torque may be generated, for example, by converting kinetic energy to electric energy. This electric energy may then be fed back, for example, to a storage battery. However, there is a maximum first braking torque that cannot be exceeded and depends, for example, on the battery charge state. If the maximum first braking torque that may be generated by the braking energy recovery arrangement is insufficient, a conventional mechanical, i.e., hydraulic, brake system is additionally activated which may generate a second braking torque, the level of which depends, for example, on the force applied to a brake pedal. The disadvantage of this method is that the pedal force needed to generate a total braking torque varies as a function of the instantaneous maximum first braking torque that may be generated by the braking energy recovery arrangement.
Because, in the braking torque regulator according to the present invention, a setpoint braking torque is supplied to the braking torque regulator, and the first breaking torque and/or second braking torque is regulated by the braking torque regulator so that an actual braking torque measured by a sensor system is used to correct the setpoint braking torque, an actual braking torque dependent on the setpoint braking torque may be generated without the instantaneous maximum first braking torque having an effect that may be felt by the driver.
The sensor system may include, for example, wheel force sensors. The use of wheel force sensors may provide that a feedback signal representing the actual forces acting upon the wheel may be generated.
The sensor system may detect the actual braking torque that is being transmitted to the road by the wheels, since, in this case, all errors occurring in the brake system, for example, are incorporated directly into the regulation result.
The setpoint braking torque may be, for example, dependent on a position of a brake actuating element and/or a force applied thereto. If the brake actuating element is designed as a brake pedal, it is possible to ensure that, regardless of the maximum first braking torque that may currently be generated, the same actual braking torque is always generated with the same pedal position or pedal force. Depending on the vehicle type, the brake actuating element may also be designed, for example, as a hand brake.
According to one example embodiment of the braking torque regulator according to the present invention, only the second braking torque generated by the mechanical brake system is regulated.
In this case, for example, the following relationship may apply to the first braking torque to be generated by the braking energy recovery arrangement:
ME=min{MS, MEMAX}, 
and the following relationship may apply to the braking torque to be generated by the mechanical brake system:
MM=MSxe2x88x92MI. 
In this case, ME represents the first braking torque to be generated by the braking energy recovery arrangement, MS represent the setpoint braking torque, MEMAX represents the instantaneous maximum first braking torque, MM represents the second braking torque to be generated by the mechanical brake system and MI represents the actual braking torque detected by the sensor system. In this example embodiment of the braking torque regulator according to the present invention, the braking energy recovery arrangement continues to perform the braking action as long as allowed by the instantaneous value of the maximum first braking torque. If, for some reason, the first braking torque to be generated by the braking energy recovery arrangement fails to act, or only incompletely acts, upon the wheel, this is compensated by the second braking torque generated by the mechanical brake system. The second braking torque is further used to generate actual braking torques that are higher than the instantaneous maximum first braking torque.
According to another example embodiment of the present invention, only the first braking torque generated by the braking energy recovery arrangement is regulated.
In this case, the first braking torque may be divided into a first braking torque component and a second braking torque component, with a selectable reserve torque being provided for setting the range of regulation. In this example embodiment, the following relationships may apply:
MVORxe2x89xa6MEMAX; 
ME=MEG+MED; 
MEG=min{MS, MEMAXxe2x88x92MVOR}; 
MED=MSxe2x88x92MI; and 
MM=max{MSxe2x88x92MEMAX, 0}. 
In this case, MVOR represents the reserve torque, MEMAX represents the current maximum first braking torque, ME represents the first braking torque to be generated by the braking energy recovery arrangement, MEG represents a first braking torque component of the first braking torque, MED represents a second braking torque component of the first braking torque, MS represents the setpoint braking torque, and MI represents the actual braking torque detected by the sensor system. In this example embodiment, the second braking torque component of the first braking torque is used to correct the setpoint braking torque. The mechanical brake system in this case is activated only if the setpoint braking torque is higher than the current maximum first braking torque which may be generated by the braking energy recovery arrangement.
The braking energy recovery arrangement may be provided in the form of an electric machine operated in generator mode. The energy generated by this electric machine may be stored, for example, at least partially in a storage battery for later use.
In addition, the electric machine may also be operated as a motor. In connection with hybrid vehicles, for example, this motor may help drive the vehicle. However, it is also possible to use the motor as a starter.
In certain example embodiments of the braking torque regulator according to the present invention, the setpoint braking torque may be influenced by a higher-level regulating device. A higher-level regulating device of this type may be, for example, an anti-lock system, a traction control system or any system which is suitable for improving driving stability.
Because a method according to the present invention includes the following steps:
a) Detection of a setpoint braking torque;
b) Provision of a sensor system and detection of an actual braking torque by the sensor system; and
c) Regulation of the first braking torque and/or the second braking torque so that the actual braking torque is used to correct the setpoint braking torque;
an actual braking torque dependant on the setpoint braking torque may be generated without the current maximum first braking torque having an effect which is noticeable to the driver.
In the method according to the present invention, step b) may include, for example, detecting the wheel forces. This makes it possible, during regulation, to take into account errors in the brake system or deviations in the braking action due to wear and tear.
Step b) may include detecting the torque transmitted from the wheels to the road as the actual braking torque. In addition, this makes it possible, for example, to take into account roadway properties.
Step a) of the method according to the present invention may include, for example, detecting a position of a brake actuating element and/or a force applied thereto. The brake actuating element may be designed as a brake pedal or hand brake, and the ease of vehicle handling may be increased, for example, by always generating the same actual braking torque with a certain pedal force, regardless of the current maximum first braking torque that may be generated by the braking energy recovery arrangement.
In one example embodiment of the method according to the present invention, only the second braking torque is regulated.
In this case, step c) may include, for example, the following substeps:
c1) Determination of the first braking torque according to the following relationship:
ME=min{MS, MEMAX}); and 
c2) Determination of the second braking torque according to the following relationship:
MM=MSxe2x88x92MI; 
where MS represents the first braking torque, MS represents the setpoint braking torque, MEMAX represents the current maximum first braking torque, MM represents the second braking torque and MI represents the actual braking torque.
According to a second example embodiment of the method according to the present invention, only the first braking torque is regulated.
In this case, step c) may include, for example, the following substeps:
c3) Definition of a reserve torque for setting the range of regulation so that the following relationship applies:
MVORxe2x89xa6MEMAX; 
c4) Determination of a first braking torque component of the first braking torque according to the following relationship:
MEG=min{MS, MEMAXxe2x88x92MVOR}; 
c5) Determination of a second braking torque component of the first braking torque according to the following relationship:
MED=MSxe2x88x92MI; 
c6) Determination of the second braking torque according to the following relationship:
MM=max{MSxe2x88x92MEMAX, 0}; 
where MVOR represents the reserve torque, MEG represents the first braking torque component of the first braking torque, MED represents the second braking torque component of the first braking torque, ME represents the first braking torque, MS represents the setpoint braking torque, MEMAX represents the current maximum first braking torque, MM represents the second braking torque and MI represents the actual braking torque.
In connection with the method according to the present invention, it is also possible for the brake energy recovery arrangement to be designed as an electric machine operated in generator mode, which is able, for example, to supply power to a storage battery.
The electric machine in this case may also be operated as a motor, for example, as a motor for a hybrid vehicle, as a starter, etc.
Method step a) may include, for example, having the setpoint braking torque influenced by a higher-level regulating device in certain vehicle operating states. This higher-level regulating device may also be formed, for example, by an anti-lock system, a traction control system, a regulating system to control vehicle stability, etc.
The present invention also relates to circuitry for a braking force controller of a vehicle which has a braking energy recovery arrangement.
In a first example embodiment of the circuit according to the present invention, the circuit has the following signal inputs and signal outputs:
A first signal input for supplying a first input signal corresponding to a setpoint braking torque;
A second signal input for supplying a second input signal corresponding to a maximum braking torque that may be generated by the braking energy recovery arrangement;
A third signal input for supplying a third input signal corresponding to a detected actual braking torque;
A first signal output for outputting a first output signal which defines a first braking torque to be generated by the braking energy recovery arrangement; and
A second signal output for outputting a second output signal which defines a second braking torque to be generated by a mechanical brake system.
In this example embodiment of the circuit according to the present invention, the first output signal is determined so that the following applies to the first braking torque:
xe2x80x83ME=min{MS, MEMAX}. 
The second output signal is determined so that the following applies to the second braking torque:
MM=MSxe2x88x92MI. 
In this case, ME represents the first braking torque, MS represents the setpoint braking torque, MEMAX represents the current maximum first braking torque, MM represents the second braking torque and MI represents the actual braking torque.
In a second example embodiment of the circuit according to the present invention, the circuit has the same signal inputs and signal outputs as in the first example embodiment. In the second example embodiment of the circuit according to the present invention, however, a reserve torque is provided for setting the range of regulation. If MVOR represents the reserve torque, MEMAX represents the current maximum first braking torque, ME represents the first braking torque, MEG represents a first braking torque component of the first braking torque, MED represents a second braking torque component of the first braking torque, MS represents a setpoint braking torque, MI represents an actual braking torque and MM represents a second braking torque, and if MVOR is less than or equal to MEMAX, the second example embodiment of the circuit according to the present invention supplies the following output signals:
The first output signal is determined so that the following applies to a first braking torque composed of the first braking torque component and the second braking torque component:
ME=MEG+MED, where 
MEG=min{MS, MEMAXxe2x88x92MVOR} and 
MED=MSxe2x88x92MI. 
The second output signal is determined so that the following applies to the second braking torque:
MM=max{MSxe2x88x92MEMAX, 0}. 